man显示命令帮助时，里面的SYNOPSIS部分释意

布满荆棘的人生 2022-06-13 00:10 126阅读 0赞

Regarding the route command, it is a little intimidating, but take it apart and analyze it. First, realize that text not in any sort of special punctuation is**required**.Anything in square brackets ( \[ \] ) is*optional*.Any text in bold is literal (must be typed in exactly that way\- sort of - it'll make sense in a second). So let me copy from the man page on my FC4 system:

黑体部分是一定要按原样填上去的,非黑体部分,如familiy,target等要用适当参数去代替的

Code:

**route** \[ **-CFvnee**\]

**route** \[ **-v**\] \[ **-A** family\] **add** \[ **-net**| **-host**\] target \[ **netmask** Nm\] \[ **gw** Gw\] \[ **metric** N\] \[ **mss** M\] \[ **window** W\] \[ **irtt** I\] \[ **reject**\] \[ **mod**\] \[ **dyn**\] \[ **reinstate**\] \[\[ **dev**\] If\]

**route** \[ **-V**\] \[ **--version**\] \[ **-h**\] \[ **--help**

Ok, the first line:

Code:

route [-CFvnee]

That says you run can invoke route with zero or more options. The stuff inside the square brackets is optional; you don't have to type them on the command line. If you do, it will alter the way the program runs. There will be a description further down in the man page that describes what each option does. The leading '-' in the set of options is an indicator that these are command line options. In this case, the command allows you to combine multiple, single letter options into one dashed option. In other words "route -n -F -C" is equivalent to "route -nFC". That is just an example. You'll need to read the descriptions of the options to know if it makes any sense to combine them in that manner.  
  
Second line:

Code:

Looks really complicated, right? It's actually not too bad. The thing to notice is the "add" toward the beginning. It's not in brackets, which means it's**required** on the command line. So why didn't the previous linehave the "add"? Think of it as a mode of operation. The first version of the command is likely a query. As the administrator, you just want to know what routes are available. However, there are times when you want to add a route to the table. This form of the command is saying you use the "add" word to tell the route command that's what you intend. When the add command is present, there are other options the program will recognize and act on (as opposed to a simple status query). Again, just to reiterate the point, anything in brackets is optional. You can put it on the command line or omit it. One thing to note though, the "-v" and "-A family" options come*before* the add command. Route will complain if you try to put them afterward. Similarly, any of the stuff listed after "add" cannot be used before "add".(命令选项及参数的顺序要遵循上面显示的顺序)  
  
So what's this: \[**-net**|**-host**\](只能选一个,或者都不选)  
That says you can have either "-net" on the command line or "-host" but you cannot have both. You can omit them both entirely, but both cannot be present on the command line at the same time.  
  
Now, you'll also notice "target" is not in bold. That's because you have toreplace it with the appropriate value to achieve whatever task you're trying to accomplish. Again, if it's in bold, it's usually literal text. If not, thenit means it's a user-supplied data/parameter/argument.  
  
All the other stuff is pretty similar. Take this guy: \[**netmask** Nm\]//如果在命令行中加了netmask，则其后面一定要接一个具体的掩码值(NM)  
That says if you supply the netmask keyword on the command line, you are obligated to include Nm, which would be the user-supplied value for the netmask.Both pieces are enclosed by the square brackets, meaning they are optional. If you include it though, you need to provide both the keyword and the associated value; you**cannot** give one and not the other.  
  
There is one last awkward looking one: \[\[**dev**\] If\]（两个层次的可选项）  
What's with the nested brackets? That's just saying  there are actually two layers of optional text. The command does not need to specify either of these options. If it does, the command can specify just the If part (omitting**dev** because it's inside nested square brackets). Or the command can specify both pieces.  
  
  
Third line:

Code:

**route** \[ **-v**\] \[ **-A** family\] **del** \[ **-net**| **-host**\] target \[ **gw** Gw\] \[ **netmask** Nm\] \[ **metric** N\] \[\[ **dev**\] If\]

I won't go over this in much detail because it's very similar to the previous line. The difference to notice is that "add" has been replaced with "del". This form of the command would delete a route from the table. Just as with the add form of the command before, there are special option that the command will recognize when deleting a route. You should notice that delete doesn't accept the same set of options that add does. They both share options, but the del version of the command does not support all of the options add does.  
  
  
Fourth line:

Code:

route [-V] [--version] [-h] [--help]

This is sort of fluff really. It's that the man page authors took the time to explicitly list the run-time help options the command supports. You will see some man pages collapse this into the first line's version of the command.